linux-kernel - Re: [PATCH v6 10/34] x86, x86/mm, x86/xen, olpc: Use __va() against just the physical address in cr3

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Date:   Thu, 8 Jun 2017 08:42:51 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        linux-arch@...r.kernel.org, linux-efi@...r.kernel.org,
        kvm@...r.kernel.org, linux-doc@...r.kernel.org, x86@...nel.org,
        kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kasan-dev@...glegroups.com, linux-mm@...ck.org,
        iommu@...ts.linux-foundation.org
Cc:     Rik van Riel <riel@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Toshimitsu Kani <toshi.kani@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Jonathan Corbet <corbet@....net>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Joerg Roedel <joro@...tes.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Larry Woodman <lwoodman@...hat.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dave Young <dyoung@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Juergen Gross <jgross@...e.com>,
        xen-devel <xen-devel@...ts.xen.org>
Subject: Re: [PATCH v6 10/34] x86, x86/mm, x86/xen, olpc: Use __va() against
 just the physical address in cr3

On 6/7/2017 5:06 PM, Boris Ostrovsky wrote:
> On 06/07/2017 03:14 PM, Tom Lendacky wrote:
>> The cr3 register entry can contain the SME encryption bit that indicates
>> the PGD is encrypted.  The encryption bit should not be used when creating
>> a virtual address for the PGD table.
>>
>> Create a new function, read_cr3_pa(), that will extract the physical
>> address from the cr3 register. This function is then used where a virtual
>> address of the PGD needs to be created/used from the cr3 register.
>>
>> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
>> ---
>>   arch/x86/include/asm/special_insns.h |    9 +++++++++
>>   arch/x86/kernel/head64.c             |    2 +-
>>   arch/x86/mm/fault.c                  |   10 +++++-----
>>   arch/x86/mm/ioremap.c                |    2 +-
>>   arch/x86/platform/olpc/olpc-xo1-pm.c |    2 +-
>>   arch/x86/power/hibernate_64.c        |    2 +-
>>   arch/x86/xen/mmu_pv.c                |    6 +++---
>>   7 files changed, 21 insertions(+), 12 deletions(-)
>>

...

>> diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c
>> index 1f386d7..2dc5243 100644
>> --- a/arch/x86/xen/mmu_pv.c
>> +++ b/arch/x86/xen/mmu_pv.c
>> @@ -2022,7 +2022,7 @@ static phys_addr_t __init xen_early_virt_to_phys(unsigned long vaddr)
>>   	pmd_t pmd;
>>   	pte_t pte;
>>   
>> -	pa = read_cr3();
>> +	pa = read_cr3_pa();
>>   	pgd = native_make_pgd(xen_read_phys_ulong(pa + pgd_index(vaddr) *
>>   						       sizeof(pgd)));
>>   	if (!pgd_present(pgd))
>> @@ -2102,7 +2102,7 @@ void __init xen_relocate_p2m(void)
>>   	pt_phys = pmd_phys + PFN_PHYS(n_pmd);
>>   	p2m_pfn = PFN_DOWN(pt_phys) + n_pt;
>>   
>> -	pgd = __va(read_cr3());
>> +	pgd = __va(read_cr3_pa());
>>   	new_p2m = (unsigned long *)(2 * PGDIR_SIZE);
>>   	idx_p4d = 0;
>>   	save_pud = n_pud;
>> @@ -2209,7 +2209,7 @@ static void __init xen_write_cr3_init(unsigned long cr3)
>>   {
>>   	unsigned long pfn = PFN_DOWN(__pa(swapper_pg_dir));
>>   
>> -	BUG_ON(read_cr3() != __pa(initial_page_table));
>> +	BUG_ON(read_cr3_pa() != __pa(initial_page_table));
>>   	BUG_ON(cr3 != __pa(swapper_pg_dir));
>>   
>>   	/*
> 
> 
> (Please copy Xen maintainers when modifying xen-related files.)

Sorry about that, missed adding the Xen maintainers when I added this
change.

> 
> Given that page tables for Xen PV guests are controlled by the
> hypervisor I don't think this change (although harmless) is necessary.

I can back this change out if the Xen maintainers think that's best.

> What may be needed is making sure X86_FEATURE_SME is not set for PV guests.

And that may be something that Xen will need to control through either
CPUID or MSR support for the PV guests.

Thanks,
Tom

> 
> -boris
>